Needle in a haystack

From Memory Alpha, the free Star Trek reference

Needle in a haystack is a Human slang term which described the long-lasting search for something in a large variety of possibilties.

In 2369 while searching for the crash-landed runabout USS Yangtzee Kiang in the Gamma Quadrant, Miles O'Brien compared the search with searching a needle in a haystack. O'Brien and Jadzia Dax had to search several planets, two dozen moons, and an asteroid belt. (DS9: "Battle Lines")